Meggers 1951–1952:Brian O'Brien 1953–1954:Deane B. Judd 1955–1957:Ralph A. Sawyer 1958:Irving C. Gardner 1959:John D. Strong 1960:James G. Baker 1961:Wallace
這導致這種看不見的濃縮物主要由白矮星和中子星組成,只有極少數的黑洞。 哈伯觀察所見的球狀星團NGC 6397 Shapley, Harlow; Sawyer, Helen B., A Classification of Globular Clusters, Harvard College Observatory
Miller, D. Gary. External Influences on English: From its Beginnings to the Renaissance. Oxford University Press. 2012. ISBN 978-0199654260. Sawyer, P. H